Greetings Roberto,
> I used 3dMVM with -glfLabel 1 level_ftest -glfCode 1 'level : 1*level_1 & 1*level_3 & 1*level_5' but I'm not sure about that.
The specification is correct. However, 3dMVM can only properly perform such an F-test for a between-subjects factor. To run such an F-test for a within-subject factor in your case, use 3dLME with the same -glfCode specification.
Gang